In the present invention, closing an openable vent hole includes changing the openable vent hole from a large opening degree to a small opening degree. Also, opening an openable vent hole includes changing the openable vent hole from a small degree of opening to a large degree of opening.
It is well known that airbags are provided with a vent hole and that, when a vehicle occupant or the like collides with an inflated airbag, an impact on such a vehicle occupant is absorbed by gas being discharged from the airbag through such a vent hole.
WO2006/041552 describes an airbag having a band (cinch tube) formed around a vent hole (aperture) so as to allow such a vent hole to be tied up. The vent hole is disposed on the side of the airbag in an inflated state, while the band is connected to the occupant side of the inflated airbag through the inside of the airbag.
In WO2006/041552, the vent hole is in an open state when the airbag begins to inflate (FIG. 5A of WO2006/041552).
As the airbag inflates and the occupant side of the airbag expands toward the occupant, the band is drawn into the inside of the airbag to tie up the vent hole, thereby causing the vent hole to be closed.
In WO2006/041552, a normally open vent hole (vent) that is in a normally open state is provided, independently of the openable vent hole that can be closed by the band as described above.
If an airbag inflates when an occupant is seated in a normal seating position or in a so-called in-position, the airbag inflates into a normal inflation completed shape. In this case, the openable vent hole is closed by being tied up with a band, as described above. When the occupant comes into contact with the airbag, gas is discharged to the outside of the airbag through the normally open vent hole (FIG. 5C of WO2006/041552).
If the airbag inflates when the occupant is seated forward from a normal seating position or in a so-called out-of-position, the occupant comes into contact with the occupant side of the airbag before the airbag inflates into a normal inflation completed shape, namely, before the openable vent hole has been closed by being tied up with the band. In this case, since the band is not further drawn into the inside of the airbag, the openable vent hole remains open, causing gas to be discharged to the outside of the airbag through both the openable vent hole and the normally open vent hole (FIG. 5F of WO2006/041552).
In the foregoing WO2006/041552, the openable vent hole remains opened when the airbag begins to inflate, which makes it difficult to allow the airbag to promptly inflate. In order to promptly inflate the airbag described in WO2006/041552, a high-power inflator must be used.